Re: Gurus? Care to re-explain the absense of gh_set_x() for me?

[Matthias Koeppe]

Sam Tregar <address@hidden> writes:

> On Fri, 13 Jul 2001, Martin Grabmueller wrote:
> 
>> Is there a particular reason you need this type of functionality?
> 
> Yes.  I need to implement "+=" type operators to work on SCMs.  These SCMs
> might or might not be bound at the top-level when the operator is called.
> I see no easy way to determine if they are since I have no way to scan the
> top-level defines.
> 
> Simple put, how can I implement this call in C:
> 
>    (+= a 10)

You should not attempt to code this as a C function.  += is not simply
a new procedure but needs to be a *special form* (i.e., a new syntax).
So I suggest you make a macro that expands (+= A B) into (SET! A (PLUS
A B)) and bind it to `+='.  In Scheme, this is easily done with
DEFINE-MACRO; if you insist in doing this from the C level, try your
luck with the functions in `macro.h'.  Then implement PLUS as a C
function that simply computes the desired value.

-- 
Matthias Köppe -- http://www.math.uni-magdeburg.de/~mkoeppe